This invention is directed to methods for the termination of post cure occurring in the thickening of siloxanes with silicone elastomers.
In the '362 patent, silicone elastomers are used in the thickening of silicone fluids and organic solvents. These elastomers are formed by a hydrosilylation reaction between a multifunctional .ident.SiH siloxane and an .alpha.,.omega.-diene.
According to the '362 patent, one scheme representative of a process that can be used in making a silicone elastomer suitable in thickening a low viscosity fluid is shown below:
Step 1--Gelation PA0 Step 2--Shear & Swell
.alpha.,.omega.-diene+.ident.Si--H Siloxane+Fluid+Pt Catalyst.fwdarw.Gel
Gel+More Fluid.fwdarw.Paste
When a network is formed in such a reaction, we have determined that steric hindrance of the crosslinked structure prevents the reaction from reaching completion. This is believed to be due to the fact that a small amount of residual functionality will remain even after long reaction times, and that unreacted functionalities will tend to meet each other when the gel is sheared and swollen. We have termed the phenomenon post cure. Because residual reactivity causes smooth pasty products to gel once again, post cure should be eliminated in order to maintain a finer appearance and a more flowable rheology of the final paste product.
This can be achieved, according to our invention, by deactivating the platinum (Pt) catalyst with an amino acid ester post cure terminating agent, most preferably a sulfur containing amino acid ester.